Apparatus for manual wire bonding

ABSTRACT

An apparatus for manual wire bonding, comprising an ultrasonically energizable and/or thermocompression wedge (11) for pressing the wire (34) against a bonding pad, wherein the wedge (11) is part of a bonding head (10) adapted to be moved towards and away from said bonding pad, especially in up/down direction. The bonding pad is disposed on a base which is movable in a direction approximately transversely to the direction of movement of the bonding head (10) for positioning the bonding pad opposite said wedge (11). Furthermore, means is provided for controlling the drive unit (20) of the bonding head. Preferably, the drive unit (20) for the bonding head motion is a d.c. servomotor, wherein each part-motion and non-motion of the bonding head (10) can be adjusted individually in respect of travelling distance and speed and motionless period, respectively, and can be checked as to execution. To this end the drive unit (20) cooperates with a distance and speed control (44-51) and feedback (28) unit.

The present invention is directed to an apparatus for manual wirebonding as specified in the preamble of claim 1.

In microelectronics, bonding generally means the interconnection ofcomponents by cementing or welding as compared to normal soldering, inwhich the connections are made by means of solder (mostly a tin-leadalloy). One distinguishes between chip (die) bonding methods formounting a component on a supporting substrate and wire bonding methodsfor connecting the component terminals to the substrate or,respectively, the contact pads of component and substrate by means offine wires.

The present invention deals with the last-mentioned method, in which theso-called thermocompression bonding or ultrasonic wedge bonding is used.The bonding wires used are gold or aluminum wires of greater or smallersize. For certain cases, thermocompression bonding and ultrasonicbonding are combined. In that case one speaks of thermosonic bonding, asit is called, in which mostly gold wire is used which, similar to ballbonding, is melted off to form a ball, and welding or bonding takesplace at a moderate heat (150° to 160° C.) by means of ultrasonicenergy. This method can be well controlled and well automated. The useof aluminium wire is a further development of the thermosonic method.Melting-off takes place under forming gas so as to obtain an oxide-freesurface. The use of the one or other bonding method dependssubstantially on the type and volume of the respective circuit design.

The above-mentioned bonding methods are mostly carried out by fullyautomatic bonding apparatus. But the hardware and software requiredtherefor is highly complex and is not necessary in many cases.

It is therefore the object of the present invention to provide anapparatus for manual wire bonding which, while causing relatively littledesign effort, is easy to handle, operates accurately and can be adaptedto a variety of external conditions.

In accordance with the invention the specified object is solved by thecharacterizing features of patent claim 1 and one or several of thefurther claims, respectively.

The significance of the invention resides in the variability andtherefore the wide variety of possible applications while beingextremely easy to handle, so that such an apparatus can also besuccessfully used in threshold countries. Moreover, the apparatusaccording to the invention is especially suited for performing bondingtests and pull tests. With the apparatus according to the invention itis also possible in an extremely simple way to determine the bondingconditions which must be observed for automated bonding. This appliesespecially to the movements to be performed by the bonding head inrespect of distance and speed and the matching of empirical compressionand/or ultrasonic and/or heating periods with the sequence of motions ofthe bonding head. At the same time, the control of the wire clamp canreadily be matched with the movement of the bonding head. The functionfeedback provided in accordance with the invention is of particularsignificance. Every single function of the bonding head is checked forproper execution. When the counter-check indicates that the function hasnot been executed, the bonding operation is interrupted and must berestarted manually. Prior to restarting, the source of error can bechecked and eliminated. Thereby it is also possible to considerablyreduce the rate of rejects, which has so far been practically impossiblewith manual wire bonding.

For moving the bonding head and controlling the movements thereof a d.c.motor is especially suited, which is due to the characteristic of saidmotor. Basically, of course, other drive units such as stepping motorscould also be used. But in all cases the counter-check of the movementsperformed by the bonding head and the movable units associatedtherewith, for instance wire clamp or vibration damping means, isimportant. Thus, the apparatus according to the invention is not onlyintended to be easily and individually adjustable but must also beadapted for checking as to each individual function.

Below, a preferred embodiment of an apparatus according to the inventionshall be described in detail with reference to the accompanying drawing,wherein it is to be noted that modifications of the described embodimentshall be within the scope of the invention. In the drawing:

FIG. 1 is a side view of the bonding head of a bonding apparatusaccording to the invention;

FIG. 2 is a front view of the bonding head of FIG. 1;

FIG. 3 is a schematic plan view showing the control panel of theapparatus according to the invention;

FIG. 4 illustrates schematically the speed control and feedback of thebonding head drive means; and

FIG. 5a-5c are flow charts of the apparatus according to the invention.

FIGS. 1 and 2 merely show a preferred bonding head design of anapparatus for manual wire bonding. This bonding head is mounted on anupright frame (not illustrated). Beneath the bonding head a base isprovided for the components etc. to be bonded. The base also is notillustrated because it is a part which is known in principle. It shouldbe noted, however, that the base is movable in a direction approximatelytransversely of the direction of movement 10 for positioning the bondingpads. The bonding head 10 comprises a wedge 11 operatively connected toan ultrasonic generator and having a wire clamp 12 associated therewith.The wire clamp 12 is mounted for reciprocating movement in longitudinaldirection of the wire or wire advancing direction relative to the wedge11. Moreover, it is biased in closing direction so that it must beopened against the biasing action in order to be movable relative to thewire without taking the wire along.

The wedge 11 is mounted on a support 14 which is mounted in the bondinghead 10 for pivoting movement about an axis 13. The support 14 isretained by a tension spring 15 in engagement with a stop 16. Againstthe action of the tension spring 15 the support 14 and thus the wedge 11are pivotable or upwardly displaceable in counterclockwise direction(arrow 17). Such displacement or pivoting movement occurs upon theso-called "touch-down" state of the wedge 11, i.e. when the wedge 11touches the bonding pad that is to be bonded. The displacement of thesupport 14 and thus the touch-down state of the wedge 11 is detected bya sensor disposed in the bonding head 10, said sensor being in the formof a light barrier 18. More concretely, the illustrated embodimentemploys a fork-type light barrier into which a projecting member 19 ofthe support 14 is extended (see FIG. 2). The light barrier 18 can beadjusted relative to the projecting member 19 such that the touch-downis indicated only when the support 14 has been pivoted about the axis 13in the direction of the arrow 17 about a predetermined angle from thezero position or engagement with the stop 16, respectively. This angledefines the so-called overdrive. It is thereby ensured that the wedge 11presses against the bonding pad with a predetermined force as determinedby the tension spring 15. At the same time the light barrier 18 producesa signal for the up/down drive unit of the bonding head 10, which willbe described later, so that the drive unit is turned off and the bondinghead 10 stops. The bonding head 10 then occupies the co-call touch-downheight, which is temporarily stored for determining the loop height.

The up/down movement of the bonding head 10 is caused by a d.c.servomotor 20 (see FIG. 2). The servomotor 20 is fixedly mounted in theupright frame (not illustrated) of the apparatus. The output shaft 21 ofthe motor 20 is coupled to an eccentric member 22. The latter is in turncoupled to an approximately vertically extending and length-variableplunger 23 whose other end, the bottom end in the present case, islinked to the bonding head 12 (link 24). In vertical direction thebonding head 10 may be guided by a linear bearing. In the illustratedembodiment the bonding head 10 is pivotable about a swivel bearing 25disposed in the frame. The pivot of this bearing is aligned with thealready mentioned pivot axis 13 for the support 14 of the wedge 11. Thepivotal movement of the bonding head 10 about the bearing 25 isillustrated by a double-arrow 26 in FIG. 1. By the way, FIG. 2 shows apart of the frame, viz. the part comprising the swivel bearing 25. Thispart is referenced 27.

The output shaft 21 of the d.c. motor 20 is mechanically coupled throughthe eccentric member 22 to a feedback potentiometer 28 secured to afixing bracket 29 which is fixed to the frame. This feedbackpotentiometer is coupled on one side to a distance comparing means andon the other side to a speed selecting means 31 the operation of whichwill be described farther below.

Moreover the servomotor has a tachogenerator 32 associated therewith fordelivering actual-speed signals to the speed selecting means 31.

In order to suppress or dampen vibrations caused by the up/down movementof the bonding head 10 and acting on the wedge 11 prior to the bondingoperation proper, the support 14 for the wedge 11 has a damping solenoid33 allocated thereto which is selectively energized and then urges thesupport 14 against the stop 16. Upon touch-down of the bonding head orduring the touch-down motion thereof the damping solenoid of course mustbe deenergized so that the support 14 can again be pivoted freely aboutthe pivot axis 13.

Guiding of the wire towards the wedge 11 through the wire clamp 12 isindicated by the line 34 in FIG. 1. The wire clamp 12 is a U-clamp 35biased towards the closed position (see FIG. 2). One leg of the U-clamp35 is coupled to a lever 36 which is mounted in the bonding head 10 forpivoting motion about a vertical axis and the diametrically opposite end37 of which is acted upon by a solenoid 38 such that, when the solenoid38 is energized, the lever 36 is pivoted while opening the wire clamp12. During this operation the lever 36 with its end coupled to the wireclamp 12 moves upwards out of the plane of the drawing in FIG. 1.

Finally, the lever 36 is also mounted in the bonding head 10 forpivoting movement about a horizontal axis extending approximatelyparallel to the pivot axis 13, the pivoting motion being limited inupward direction by a stop 39 and in downward direction by a stop 40.The pivoting motion of the lever 36 and thus of the wire clamp 12 in avertical plane is caused by a solenoid or electromagnet 41 against theaction of a tension spring 42, the tear-off spring as it is called. Theupper stop 39 defines the so-called zero position of the wire clamp 12.With the lower stop 40 the wire tail length is adjusted. Each of thestops 39 and 40 is disposed in positionally variable fashion in thesupport 14 for the wedge 11. The lever 36 as well as the solenoid 38,the solenoid 41 and the stops 39, 40 and the tear-off spring 42 formpart of the pivotally mounted support 14. The horizontal pivot axis ofthe lever 36 is defined by the pivot axis 43 of the wire clamp 12 at theforward or freely accessible end of the support 14. This pivot axis 43extends approximately parallel to the pivot axis 13 of the support 14within the bonding head 10.

The lever 36 has a further solenoid 44 associated therewith whosearmature is connected to a projecting plunger 46. When the solenoid 44is energized the plunger 46 is moved to such a position that themovement of the lever 36 about the pivot axis 43 in FIG. 1 is downwardlylimited. The corresponding position of the plunger 46 is indicated indashed lines in FIG. 1. The limitation of the pivoting movement of thelever 36 and thus of the wire clamp 12 becomes effective whenever thewire clamp 12 is intended to be moved to the wire tear-off position. Tothis end the wire clamp 12 in its open position is moved to the right inFIG. 1 relative to the wire 34 without taking the same along (the wireclamp 12 rotates counterclockwise about the axis 43). This relativemovement of the wire clamp 12 is limited by the extended plunger 46(shown in dashed lines in FIG. 1). When the wire 34, after having beenfixed to the bonding pad, is to be torn off with the wedge 11 still inengagement, the solenoid 41 is merely deenergized and consequently thelever 36 is abruptly pulled upwards in

FIG. 1 by the tear-off spring 42 while simultaneously the wire clamp 12is pivoted in clockwise direction about the axis 43. Before that,however, the wire clamp 12 is moved to the closed position.

Below, the operation of the bonding apparatus according to the inventionshall be described:

The distance comparing means 30, which is operatively connected to boththe drive unit 20 and the feedback potentiometer 28, has four distancepotentiometers 44, 45, 46 and 47 allocated thereto by which thefollowing settings are provided:

potentiometer 44: fixing of the starting position or starting height ofthe bonding head 19 above the base carrying the bonding pad;

potentiometer 45: fixing of the first search position or search height(H1) of the bonding head 10;

potentiometer 46: fixing of the second search position or search height(H2) of the bonding head 10;

potentiometer 47: fixing of the loop height.

The speed selecting means 31 likewise has four potentiometers allocatedthereto, viz. the speed potentiometers 48, 49, 50 and 51. By means ofthe potentiometer 48 the movement of the bonding head 10 to the startingposition set by potentiometer 44 is initiated, where at the same timethe rate of motion is fixed by the potentiometer 48.

The touch-down speed is fixed by the potentiometer 49. The potentiometer50 is used to fix the up-and-down speed of the bonding head 10, theheight is defined as the touch-down height.

Finally, the so-called "loop" speed of the bonding head 10 is set by thepotentiometer 51. The potentiometers are disposed on a control panel asshown in FIG. 3. This control panel also includes a reset switch 52 anda start button 53. When the start button 53 is depressed the bondinghead 10 should be lowered from the starting position 54 to the firstsearch height 55. The first search height of the bonding head 10 is setby the potentiometer 45. The actual lowering of the bonding head isdetected by the feedback potentiometer 28. This actual-valve signal iscompared in the distance comparing means 30 with the desired value setby the potentiometer 45. If the actual height does not correspond to thepreset desired height, the bonding operation will be discontinued (stop56 in Fig, 5a). The bonding operation can then be restarted by actuationof the reset switch 52, commencing from the starting position 54. But ifthe actual value coincides with the desired value, the bonding head willwait at the first search height for as long as the start button 53 isbeing depressed (waiting position 57 in FIG. 5a). During this time thefirst pad to be bonded (not illustrated) is manually positioned oppositethe wedge 11 on the base, which is movable in x- and y-directions. Afterpositioning of the first bonding pad the start button 53 is released sothat the bonding head is lowered further at reduced speed, the so-calledtouch-down speed, until it touches the first bonding pad. Thistouch-down motion of the bonding head 10 is referenced 58 in FIG. 5a. Atthe beginning of the touchdown motion the damping solenoid 33, which wasenergized upon lowering of the bonding head 10 to the first searchheight 55, is deenergized so that upon touch-down of the wedge 11 on thefirst bonding pad the wedge 11 together with the support 14 may pivotabout the axis 13 in FIG. 1 in anti-clockwise direction until thetouch-down 59 is detected by the fork-type light barrier 18, so thatthen the motor 20 is turned off. In the touch-down position the wedge 11is pressed against the bonding pad with a force which is determined bythe tension spring 15. The touchdown position of the bonding head 10 isfurthermore temporarily stored in a memory. Via the feedbackpotentiometer 28 a counter-check is made to determine whether thebonding head 10 after the touch-down signal from the forktype lightbarrier 18 has actually stopped. If this is not the case, a stop 61 ofthe bonding operation takes place so that the bonding operation must berepeated by depressing the reset switch 52. In that case the bondinghead 10 would be moved to the starting position 54 again. But when thefeedback potentiometer 28 indicates that the vertical motion of thebonding head 10 coincides with the touch-down signal the drive unit 20is instructed by a programme unit 62 to remain in the touch-downposition, for instance for a period of 40 ms. It is thereby achievedthat during bonding the wedge 11 no longer performs any vibrationscaused by the touch-down movement, i.e. that the wedge is absolutelystill. The rest period of the bonding head upon touch-down is referenced63 in FIG. 5a. When this rest period has elapsed, the transducerassociated with the wedge 11 is instructed by the programme unit 62 toperform ultrasonic vibrations, which is done on a first channel. Theseultrasonic vibrations are adjusted as to time and intensity (preferablyby manual adjustment).

This process is discontinued by an "end" signal. If the programme unitdoes not detect such an "end" signal the bonding operation will bestopped (stop 64 in FIG. 5a). Upon indication of the ultrasonicenergy-end signal the bonding head 10 is elevated to the so-called loopheight 65 set by the loop potentiometer 47. The loop height 65 is aconstant setting based on the temporarily stored (memory 60) touch-downheight 59. The bonding head 10 is elevated at the loop speed. Throughthe feedback potentiometer 28 it would again be possible to checkwhether the bonding head 10 actually has moved through the set distance,based on the temporarily stored touch-down height. If not, the bondingoperation could again be stopped and could be restarted via the resetswitch 52.

When the bonding head 10 is at the loop height 65, the start button 53is again depressed in the flow chart illustrated as an example in FIGS.5a to 5c, and consequently the bonding head 10 is lowered to the secondsearch height 66 in which it finally remains. The lowering is performedat increased up-and-down speed as set by the potentiometer 50. By meansof the feedback potentiometer 28 and the distance comparing means 30 acomparison between actual and desired values is made again. When thebonding head 10 has not reached the second search height set by thepotentiometer 46 a stop signal 67 occurs and consequently the bondingoperation would have to be restarted by depressing the reset switch 52.Upon coincidence of actual and desired values and when the secondbonding pad is positioned opposite the wedge 11, the start button 53 maybe released again so that the bonding head 10 is lowered onto the secondbonding pad, which again occurs at the reduced touch-down speed untilthe fork-type light barrier 18 has detected the touch-down state on thesecond bonding pad. Upon receipt of this signal the motor 20 is stopped.If the actual movement of the bonding head 10 is not in conformity withthe touch-down signal the bonding operation will be stopped (stop 68 inFIG. 5b with the consequences already described above). For the rest,the drive unit 20 is again supplied by the programme unit 62 with a restsignal 69 of e.g. 40 ms so that the wedge 11 touching the bonding pad ismade absolutely still. When the bonding head 10 or the wedge 11 has beensteadied the transducer is instructed on channel 2 to perform ultrasonicvibrations. This means that time and intensity may be selected to bedifferent as compared to the ultrasonic vibrations on channel 1. Theinstruction to the transducer is delivered by the programme unit 62. Theultrasonic vibrations are made to stop by an ultrasonic energy-endsignal. If this does not occur after a predetermined period of time, thebonding operation will be stopped (stop 70 in FIG. 5c). Following theultrasonic energy-end signal the solenoid 38, which is responsible foropening the wire clamp 12, is instructed to close the wire clamp 12.Thereupon the solenoid 41 responsible for the movement of the wire clamp12 in the direction of the bonding wire 34 is instructed to release thewire clamp 12 so that it is abruptly pulled by the tear-off spring 42 tothe tear-off position while at the same time the wire 34 is torn off thebonded wire length. While this happens, the wedge 11 of course remainsin contact with the second bonding pad and presses the bonded wireagainst the same. Subsequently, the bonding head 10 is again moved tothe starting position set by the potentiometer 44, whereby a bondingcycle has been completed.

FIG. 4 illustrates schematically in what way the tachogeneratorassociated with the drive unit 20 is coupled to the speed selectingmeans 31. By means of the potentiometers 48-51 the speeds of the bondinghead for certain sub-motions are fixed. The tachogenerator 32 detectswhether the preset speeds are observed; if not, a correspondingcorrection will be made. By means of the feedback potentiometer 28,which is likewise coupled to the speed selecting means 31, thechange-over points for the differently selected speeds are determined,on the one hand, and on the other hand the approach of the bonding headto a preset final position is indicated so that a correspondingdecelerrating signal can be delivered to the motor 20. The feedbackpotentiometer 28 therefore has multiple functions and is essential forthe sequence of motions and functions of the apparatus according to theinvention.

The programme unit 62 is additionally coupled to the distancepotentiometers 44-47 so that, when predetermined bonding head heightshave been reached and have been confirmed by the feedback potentiometer28, corresponding instructions can be delivered to the transducer and/ora wedge heating means and to the actuating elements (solenoids 38, 41,44) associated with the wire clamp 12.

It will be apparent from FIGS., 5a to 5c that, when the start button 53is depressed and the bonding head 10 is lowered to the first searchheight 55, the wire clamp 12 is instructed to take the so-called "taillength" position. During the rest period 63 the wire clamp is opened andmoved to the initial position. When the start button 53 is againdepressed and the bonding head 10 is lowered from the loop height 65 tothe second search height 66, the wire clamp 12 is again instructed toclose and to move to the tear-off position. When the second searchheight has been reached the wire clamp 12 is re-opened. The furtherinstructions to the wire clamp 12 subsequent to the second bondingoperation have been described above with reference to FIG. 5c.

The transducer, which is allocated to the wedge 11 and has beenmentioned several times, is referenced 71 in FIG. 1.

It should be noted again that the described flow of operations serves asan example only and that a greater or lesser number of feedbackfunctions may be used depending on the requirements, in particularquality requirements, made on the bonding method. Above all it ispossible that, when a deviation of the actual speeds from the desiredspeeds is detected by the tachogenerator 32 or when a predeterminedthreshold-level deviation occurs, the bonding operation is discontinuedand must be restarted by actuation of the reset switch 52.

All of the features disclosed in the present documents shall be claimedas being essential to the invention to the extent to which they arenovel over the prior art either individually or in combination.

I claim:
 1. An apparatus for manual wire bonding, comprising anultrasonically energizable and/or thermocompression wedge (11) forpressing the wire (34) against a bonding pad, wherein the wedge (11) ispart of a bonding head (10) adapted to be moved towards and away fromthe bonding pad, especially in up/down direction, and the bonding pad isdisposed on a base which is movable in a direction approximatelytransversely to the direction of movement of the bonding head forpositioning the bonding pad opposite the wedge (11), and comprisingcontrol unit means for controlling a drive unit (20) for the bondinghead (10), characterized in that the bonding head (10) is adapted to bemoved by the drive unit, said drive unit including a d.c. servomotor(20), in accordance with the following cycle:(a) lowering of the bondinghead (10) from an elevated starting position (54) to a first searchposition (55); (b) after positioning of a first bonding pad opposite thewedge (11), further lowering of the bonding head (10) onto the samewhile compressing the bonding wire (34) thereagainst; (c) lifting of thebonding head (10) from the first bonding pad while moving the head to apredetermined loop position (65); (d) lowering of the bonding head (10)to a second search position (66); (e) after positioning of a secondbonding pad opposite the wedge (11), further lowering of the bondinghead (10) onto the same while compressing the bonding wire (34)thereagainst; (f) lifting of the bonding head (10) to the startingposition (54) after previously severing the bonded wire length, whereinsaid control unit means includes a distance control unit (44-47), aspeed control unit (48-51), and a distance and speed feedback unit (28)so that each part-motion and non-motion of the bonding head (10) can beadjusted individually in respect of travelling distance and speed andmotionless period, respectively, and can be checked for execution,saidcontrol unit means further includes: (a) a manually actuated switch(start button 53) for initiating the bonding head motion, (b) distancepotentiometers (44, 45, 46, 47) for setting the starting position orheight (54), the first search position or height (55), the second searchposition or height (66), and the loop position or height (65), (c) speedpotentiometers (48, 49, 50, 51) for setting the speed of the bondinghead (10) from the starting position (54) to the first search position(55), from the first search position (55) to the first "touch-down"position, from the first "touch-down" position to the loop position(65), from the loop position (65) to the second search position (66),from the second search position (66) to the second "touch-down"position, and from the second "touch-down" position back to the startingposition (54), wherein the speed potentiometers (48, 49, 50, 51) arecoupled to the drive unit (20) via a speed selecting means (31), andwherein, the distance feedback unit comprises a feedback potentiometer,which is preferably mechanically coupled to the output (output shaft 21)of the drive unit (20), the output of said potentiometer being coupledto a distance comparing unit (30) in which the desired values set by thedistance potentiometers (44, 45, 46, 47) are compared with theactualmotion values detected by the feedback potentiometer (28) toproduce an error signal (NO) or a correct signal (YES), and wherein, thespeed selecting means (31) associated with the speed potentiometers (48,49, 50, 51) is coupled on the one hand to the feedback potentiometer andon the other hand to a tachogenerator (32) serving as a speed feedbackunit (32), wherein the feedback potentiometer defines the speedchange-over points and the tachogenerator (32) detects the actual speedof the bonding head motion so that upon a deviation from a presetdesired speed a correction or interruption of the bonding operation willbe possible.
 2. An apparatus as claimed in claim 1, characterized inthat a reset means (reset switch 52) is providing for returning thebonding head (10) to the starting position (54) in response to adistance, speed and/or non-motion error signal.
 3. An apparatus asclaimed in claim 1, characterized in that a memory (60) is provided forsorting the "touch-down" height of the first bonding pad from which thepreset loop height (65) can be determined.
 4. An apparatus as claimed inclaim 1 characterized in that the wedge (11) is mounted in the bondinghead (10) for movement, especially pivoting movement, approximately inthe moving direction of said head, the wedge upon touch-down on thebonding pad being movable against the action of a resilient member (e.g.tension spring 15) from a zero position defined by a stop (16) to a"touch-down" position.
 5. An apparatus as claimed in claim 4,characterized in that the movably mounted wedge (11) cooperates with alight barrier sensor (18) for detecting the relative motion of the wedge(11) upon "touch-down" and for producing a movement stop signal for thedrive unit (20) of the bonding head (10).
 6. An apparatus as claimed inclaim 5, characterized in that a predetermined relative distance(overdrive) of the wedge (11) can be set by the sensor (light barrier18).
 7. An apparatus as claimed in claim 1, characterized in that thewedge (11) which is movably mounted in the bonding head (10) cooperateswith a vibration damping means acting on the wedge (11) or the support(14) therefor, respectively, wherein the vibration damping means isactive during movement of the bonding head (10) from the startingposition (54) to the first search position (55) and, respectively,during movement of the bonding head (10) from the loop position (65) tothe second search position (66).
 8. An apparatus as claimed in claim 1,characterized in that a programme or command unit (60) coupled to the"feedback" potentiometer (28) is associated with a wire clamp (12)cooperating with the wedge (11) and with the actuating elements foropening and closing said clamp (solenoid 38) and for moving the clamprelative to the wedge (11) (solenoids 41, 44) in the direction of thebonding wire (34) extending through said wire clamp (12), the mentionedactuating elements (solenoids 38, 41, 44) being controlled by saidprogramme or command unit (60).
 9. An apparatus as claimed in claim 1,characterized in that the bonding head (10) is movable in up/downdirection by means of a link mechanism or by means of a plunger (23)having one end coupled to the bonding head (10) and the other endcoupled to an eccentric member (22) rotatably driven by the drive motor(20).